Bing-Xin Jiang1, Hui Chen1, Wen-Jing Zhang1, Jin-Hua Lan1, Tian-Xi Yang2, Chang Lin1,2, Zhong-Hang Huang2, Kai-Xin Zhang1, Xue-Qi Zhu1, Jun He1, Yi-Fan Yang1, Yong-Ai Zhang1,2, Qun Yan1,2 and Jie Sun4,1,2,3
Published 4 April 2024 • © 2024 IOP Publishing Ltd
Engineering Research Express, Volume 6, Number 2
Citation Bing-Xin Jiang et al 2024 Eng. Res. Express 6 025303
DOI 10.1088/2631-8695/ad3610
Author e-mails
yangtianxi@126.com
jie.sun@fzu.edu.cn
Author affiliations
1 National and Local United Engineering Laboratory of Flat Panel Display Technology, College of Physics and Information Engineering, Fuzhou University, Fuzhou 350100, People’s Republic of China
2 Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China, Fuzhou 350100, People’s Republic of China
3 Quantum Device Physics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg 41296, Sweden
Author notes
4 Author to whom any correspondence should be addressed.
ORCID iDs
Bing-Xin Jiang https://orcid.org/0009-0008-2062-1054
Qun Yan https://orcid.org/0000-0002-7057-2755
Jie Sun https://orcid.org/0000-0002-6479-7771
Dates
Received 3 January 2024
Revised 7 March 2024
Accepted 20 March 2024
Published 4 April 2024
Abstract
Indium (In) is currently used to fabricate metal bumps on micro-light-emitting diode (Micro-LED) chips due to its excellent physical properties. However, as Micro-LED pixel size and pitch decrease, achieving high-quality In bumps on densely packed Micro-LED chips often presents more challenges. This paper describes the process of fabricating In bumps on micro-LEDs using thermal evaporation, highlighting an issue where In tends to grow laterally within the photoresist pattern, ultimately blocking the pattern and resulting in undersized and poorly dense In bumps on the Micro-LED chip. To address this issue, we conducted numerous experiments to study the height variation of In bumps within a range of photoresist aperture sizes (3 μm −7 μm) under two different resist thickness conditions (3.8 μm and 4.8 μm). The results showed that the resist thickness had a certain effect on the height of In bumps on the Micro-LED chip electrodes. Moreover, we found that, with the photoresist pattern size increasing under constant resist thickness conditions, the height and quality of the bumps significantly improved. Based on this finding, we rationalized the adjustment of the photoresist pattern size within a limited emission platform range to compensate for the height difference of In bumps caused by different resist thicknesses between the cathode and anode regions. Consequently, well-shaped and dense In bumps with a maximum height of up to 4.4 μm were fabricated on 8 μm pitch Micro-LED chips. Afterwards, we bonded the Micro-LED chip with indium bumps to the CMOS chip, and we found that we could successfully control the CMOS chip to drive the Micro-LED chip to display specific characters through the Flexible Printed Circuit (FPC). This work is of significant importance for the fabrication of In bumps on Micro-LED chips with pitches below 10 μm and subsequent bonding processes.
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